The principal goal of the Virology Core is to provide virological support for Projects 1`through 4 and the Immunology Core. This will be accomplished in 3 specific aims. Aim 1. To provide standardized viral stocks for in vitro assays and macaque challenge studies. Titered viral stocks for challenge will include SHIVs, provided by Dr. Yichen Lu, Virus Research Institute., Cambridge, MA., for Projects 1 through 3 and HIV- 2SBL6669, provided by Dr. G. Biberfeld, Stockholm, Sweden, for Project 4. In addition, strains of HIV-1, vaccinia constructs, and transforming herpes viruses will be grown and provided as needed to the projects and Immunology Core. Genetically, monotypic viruses obtained by transfection of infectious molecular clones will be provided as needed to ascertain the fine specificities of immune responses. The IHV has a library of infectious molecular clones and appropriate vector systems available for this purpose. Aim 2. To evaluate challenged rhesus macaques for infectious. Infection will be monitored by plasma p24/27 antigen, virus co-cultivation, and by quantitative plasma viral RNA measurements. For Projects 1 through 3, a NASBA method that detects SIV gag sequences will be used. Project 4 uses HIV-2SBL6669 as the challenge virus and a HIV-2 specific NASBA is under development by our collaborators. Alternatively, QC-PCR will be used to determine viral loads for this virus. In addition to these methods, it may be of interest to determine the phenotype or genotype of viruses that break through vaccination (c.f., Projects 1 and 3). The Virology Core will isolate these viruses and characterize relevant phenotypes and genotypes. Aim 3. TO carry out assays for neutralizing antibodies and to quantify VSFs. Neutralizing antibody assays will be carried out by the Virology Core. Several assays are online that detect antibodies specific for primary isolates and laboratory strains of virus. The Virology Core will also quantify VSF activity in supernatants provided by the Immunology Core. These assays will be overseen by Mr. Mike Merges, who has extensive experience in the performance and interpretation of such assays.